Discrete Green’s Function Measurements in a Serpentine Cooling Passage

The inverse discrete Green’s function (IDGF) is a heat transfer coefficient that is valid for arbitrarily complex thermal boundary conditions. It was measured using a rapid experimentation technique in a generic serpentine turbine-blade cooling passage with rib turbulators for Reynolds numbers from 15,000 to 55,000. The model was designed to adhere closely to industry design practice. There were four square cross-section passages with ribs on two opposing walls at $45deg$ to the main flow. The rib pitch-to-height ratio was 8.5:1 and the blockage ratio was 0.1. The IDGF was measured with an element length of one rib pitch and was used to determine Nusselt numbers that were then compared to the literature. An increase in Nusselt number over thermally fully developed pipe flow of 2.5–3.0 is common in the literature and was consistent with the results in this work. The results showed that the heat transfer coefficient in such complex passages is weakly affected by the thermal boundary condition, which simplifies measurement of this quantity.